"Who am I? I'm Minji's dad!" Cracked heels and hunched shoulders. An ordinary middle-aged man who embodies the word 'breadwinner' more than anyone else. The most precious person to him is his daughter, Minji, whom he has raised alone since losing his wife. He always feels sorry for his daughter growing up without a mother, but due to his naturally blunt personality, he is clumsy at expressing his feelings. Nevertheless, his love for his daughter is that of a 'daughter-fool' who wouldn't lose to any other father in the world. He bickers with Minji, who is in the middle of puberty, but they spend precious days understanding each other in their own ways. One day, while their ordinary life continues, Minji disappears, and he reveals his identity—which he had to keep hidden at all costs—to save her from danger. North Korea's number one most wanted, and a man whose very existence is a diplomatic crisis. The uncontrollable North-South operative, Code 66. An invisible man at the office, a dangerous person in the past. A monster searching for his daughter in the present. His name is Manager Kim.

"Feel the same pain as the people you've committed violence against." A handsome middle-aged man with long legs and slender proportions. A former Taekwondo Olympic gold medalist and a legendary martial artist with overwhelming talent who won the Taekwondo World Championships three times in a row. He was a Taekwondo star representing the Korean Peninsula, but now he runs a neighborhood Taekwondo dojo and teaches children. As a martial artist who has practiced Taekwondo his whole life, he maintains his composure in most situations, but the only thing he cannot remain calm about is his son, Seong Taehun. Because of his son, who is constantly getting into trouble, Hansu's heart doesn't have a single day of peace. When Manager Kim visits and delivers the news that his daughter Minji has been kidnapped, Hansu joins Manager Kim's journey because he, too, is a father.

"He's not a daughter-fool, he's just a fool." He has a sturdy build that looks like he could wrestle an ox, and a boisterous nature that shakes the surrounding air when he laughs. In the past, he was a soldier representing the special forces 'Cheonsan Unit,' a living witness of the battlefield who experienced several civil wars across West Asia, the Middle East, and Africa. Now, having no work, he often does traffic volunteering at an elementary school during dismissal. He says being Park Dabin's dad is the proudest thing in his life, and he is called just a fool beyond being a daughter-fool. The moment he hears that Manager Kim's daughter Minji has been kidnapped, he stands by Manager Kim's side without a moment's hesitation, as if his own daughter Dabin were in danger.

"If this happens again, both the school and you people will disappear." A legend of the bottom who started as a hired thug and swallowed up a construction company. He opened paths with violence and solidified his position with money. He leads a security organization composed of mercenaries from special forces. If money doesn't work, he uses violence; if violence doesn't work, he erases the very existence of the target from the world. He is ruthless to others and harsh to his enemies, but he is a father more tender than anyone else in front of his daughter, Joo Hyeri. He kidnaps Minji to cover up Hyeri's wrongdoing, but in his confrontation with Manager Kim, who is tracking Minji, he senses it intuitively. That this is an opponent who cannot be tamed by anything. Ultimately, he makes the wrong choice of elimination instead of conciliation, and complete erasure instead of a cover-up.

Park Jincheol's daughter. She seems to dislike her dad, but she actually likes him a bit. A 2nd-year student at Songin High School.

A delinquent. But he has a bit of a tsundere style. A 2nd-year student at Songin High School. Seong Hansu's son.

Manager Kim's daughter. A 2nd-year student at Songin High School. "Why did you even have me if you were going to be like this!" An ordinary high schooler who looks like her mom and has a personality like her dad. Since her birthday is the anniversary of her mother's death, every time her dad looks at her mom's photo, she feels guilt, wondering, 'Would Mom be alive if I hadn't been born?' Even when she is ignored and bullied at school for being from a single-parent family, she has a firm heart that rarely bows its head. After fighting back against Joo Hyeri, who looked down on her for being from a single-parent family, she sees her father, who was called to the school, kneeling before Joo Hyeri's parents. For the first time, she snaps at her father, saying, "If you were going to do this, you shouldn't have had me." Afterward, she is kidnapped and placed in a life-or-death crisis, but she is a strong girl who endures until the end, thinking of her father who will be waiting for her.